Question

why should you chock (block) the wheels of a tractor - trailer before loading or unloading?
the trailer could move away from the loading dock.
the dock board may not fit between the loading dock and trailer.
the wheels do not need to be chocked.
the lift truck could go through the floor of the trailer.

Explanation:

Chocking the wheels prevents the trailer from moving. If it moves, it could detach from the loading dock, causing safety hazards. The other options are either incorrect (wheels do need chocking for safety, dock - board fit is not the main reason, and lift - truck floor penetration is not related to wheel chocking in this context).

Answer:

The trailer could move away from the loading dock.